1. Field of the Invention
The present invention relates to a circuit diagram creating method and circuit diagram creating apparatus for a CAD apparatus for creating a layered electric circuit diagram.
2. Description of the Related Art
For a CAD apparatus for creating a circuit diagram, it is a common practice to describe a circuit diagram with layers taking into account logical consistency and repeatability, etc. In this case, as shown in FIG. 1, lower-layer drawings are normally schematized as rectangular boxes and arranged in a higher layer (in the following explanations, a lower-layer drawing schematized as a rectangular box will be called a “symbol”). In the example shown in FIG. 1, symbols with instance names NANDOR1 and NANDOR2 are described together with a cell name NANDOR. Thus, lower layers are expressed as black boxes and it is only possible to see higher-layer drawings and not possible to know the contents of the lower layers.
As a method for solving the problem that it is not possible to see the contents of a lower layer from a higher-layer drawing, there is a proposal for a method of displaying the contents of a lower layer in a symbol as shown in FIG. 2. However, since this method adopts a structure in which a circuit diagram is miniaturized and pasted so as to describe all information on the lower layer in the symbol, the circuit diagram is too small, has insufficient readability and cannot be actually used.
The invention described in Japanese Patent No. 2657028 is one that is capable of displaying how the circuits are related to each other among electric circuits of different blocks which are hierarchically expressed in an easily understandable way. This invention determines whether blocks are shown in a symbol form or schematic form according to a ratio of the block size shown on a display screen to the size of the display screen.
Of the above described conventional technologies, the one shown in FIG. 2 in which the circuit diagram is miniaturized and pasted so as to describe all information on the lower layer in the symbol, has a problem that it has insufficient readability.
The technology described in Japanese Patent No. 2657028 differentiates the display contents of the block according to the ratio of the block size shown on the display screen to the size of the display screen, and can thereby improve readability, whereas it does not always display necessary contents and has a problem that it is difficult to understand connection relations among electric circuits.